Direct digital encoding and radio frequency modulation for broadcast television applications

ABSTRACT

A digital audio encoder, digital video conditioner, and a digital modulator are described for producing a television broadcast signal at a desired channel frequency range. Left and right audio channel signals are digitized and encoded according to a stereo standard and then combined to form a stereo audio signal. A second audio programming channel signal may be included. A video input can be digitized and conditioned to form a digital video channel. The stereo audio signal can be placed directly at a desired channel frequency by frequency modulation without the need for using an intermediate frequency. The digital video channel can be placed at a desired frequency by amplitude modulation. The digital and audio channels can be digitally combined to create a television transmission signal at a desired frequency and according to a desired standard.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/228,066 filed Sep. 16, 2006, which application claims priority toU.S. Provisional Patent Application Ser. No. 60/610,915, filed Sep. 17,2004; the entire contents of both applications are incorporated hereinby reference.

BACKGROUND

There are may different kinds of television video signals, the format ofwhich varies from country to country. In the United States and Japan,for example, the NTSC format is used. NTSC stands for NationalTelevision Systems Committee, which is the name of the organization thatdeveloped the standard. In Europe, the PAL format is common. PAL standsfor phase alternating line. SECAM is a standard used in France andstands for sequential colour avec memoire (sequential color withmemory). It should be noted that there are about 15 differentsub-formats contained within these three general formats. Each of theseformats is not generally compatible with the others. Although they allutilize the same basic scanning system and represent color with a typeof phase modulation, they differ in specific scanning frequencies,number of scan lines, and color modulation techniques.

For whatever type of television video standard employed, there are threebasic levels of baseband video signal interfaces. In order of increasingquality, they are composite (or CVBS), which uses one wire pair; Y/C (orS-video), which uses two wire pairs; and component, which uses threewire pairs. Each wire pair consists of a signal and ground wire. Thesethree interfaces differ in their level of information combination (orencoding). More encoding typically degrades the quality but allows thesignal to be carried on fewer wires. Component signals have the leastamount of encoding and composite signals the most.

Composite signals are the most commonly used analog video interface.Composite video is also referred to as CVBS, which stands for color,video, blanking, and sync, or composite video baseband signal. Itcombines the brightness information (luma), the color information(chroma), and the synchronized signals on just one cable.

The Y/C signal, often referred to as “S-video,” is a less encoded videosignal. Brightness (luma), which is the Y signal, and the color(chroma), the C signal, are carried on two separate sets of wires.

Component signal interfaces are the highest performance, because theyhave the least encoding. The signals exist in nearly native format. Theyalways utilize three pairs of wires that are typically in either a luma(Y) and two-color difference-signals format or a red, green, blue (RGB)format. RGB formats are almost always used in computer applications,whereas color-difference formats are generally used in televisionapplications. The Y signal contains the brightness (luma) andsynchronizeing information, and the color-difference signals contain thered (R) minus the Y signal and the blue (B) minus the Y signal. Thetheory behind this combination is that each the base R, G, and Bcomponents can be derived from these difference signals. Commonvariations of these signals are as follows:

(1) Y, B-Y, R-Y: Luma and color-difference signals.

(2) Y, Pr, Pb: Pr and Pb are scaled versions of B-Y and R-Y.

(3) Y, Cr, Cb: Digital signal equivalent to Y, Pr, Pb.

(4) Y, U, V: intermediate quadrature signals used in the formation ofcomposite and Y/C signals.

Audio stereo signal standards for television broadcasts include MTS,standing for Multichannel Television Sound also know at the BTSCstandard. This is one of the first developed stereo sound systems. BTSCis used in conjunction with NTSC/525, mainly in North America and partsof South America. BTSC, or MTS, comprises two, and sometimes threeseparate signals for transmitting stereo audio. The first signal isformed as the sum of the left and right audio signals, and can bedetected by both monophonic television receivers (to preservecompatibility with such receivers) and stereo receivers. The secondsignal is formed as the difference between the left and right audiosignals, and is detectable only by stereo receivers. In many cases, athird signal, the Secondary Audio Program (SAP), provides for a secondlanguage or a descriptive commentary for the blind.

The FM-FM standard is used in Germany, Austria, Holland, Switzerland andAustralia. This standard uses a twin channel to transmit analog FMstereo transmissions. Like BTSC, the secondary channel can be used totransmit a second language. NICAM, stands for Near InstantaneouslyCompanded Audio Multiplex NICAM, officially called NICAM 728 and is usedthroughout Europe and Asia. NICAM is a digital two-channel audiotransmission system with a sub-code selection of bilingual operation.Because it is digital, playback is that of near Compact Disc quality.EIAJ, standing for the Electronics Industry Association of Japan, wasdeveloped and is used in Japan. EIAJ systems use a subcarrier within themain FM audio carrier. The subcarrier is an FM subcarrier rather thanthe suppressed AM subcarrier used in the BTSC system or in FM radiobroadcasting. Zweiton is a digital stereo standard that was developedout of A2 German Stereo and is used throughout Europe and Asia. Like theother systems, Zweiton has a main carrier signal and a secondary carriersignal usually used for the audio of a second language.

The television broadcast systems and standards described generally haveemployed analog and mixed analog-digital architectures to place theinput audio and video signals onto intermediate (IF) frequencies. Theuse of IF frequencies and analog architectures has presented problemsfor use in digital television applications, including the requirementfor intricate and costly filter topologies.

SUMMARY

In accordance with an aspect of the disclosure, a system for producing atelevision broadcast channel includes a digital video conditioner thatis configured to receive a digitized broadcast-compatible video signaland to produce a conditioned video signal and a pilot signal. The systemincludes a digital encoder configured to receive at least two digitizedaudio signals and the pilot signal and to produce a combined audiosignal. A digital modulator is part of the system and is configured toreceive the conditioned video signal and the combined audio signal. Thedigital modulator is configured to (a) provide frequency modulation tothe combined audio signal without the need to place the signals intointermediate frequencies, (b) provide amplitude modulation to theconditioned video signal, and (c) combine the combined audio signal andconditioned video signal to produce a complete broadcast transmissionsignal.

In one embodiment, the television further includes a digital-to-analogconverter operatively coupled to the digital modulator and configured toreceive the broadcast transmission signal and convert the broadcasttransmission signal to an analog format. The system may include ananalog-to-digital stage operatively coupled to the digital videoconditioner and configured to convert an analog broadcast-compatiblevideo signal to the digitized broadcast-compatible video signal. Thedigital video conditioner may be configured to receive a video signalcomplying with a standard selected from a group of standards includingNTSC, the PAL, PAL I, PAL B, PAL G, PAL H, PAL M, PAL D, PAL N, SECAM,SECAM D, SECAM K, SECAM L, SECAM B, and SECAM G. The digital stereoencoder may be configured to receive audio signals complying with agroup of standards including BTSC, dual-FM, EIA-J, and NICAM.

In accordance with another aspect of the disclosure, a system isprovided for producing a television broadcast signal. The system mayinclude an audio digitizing stage configured to receive left, right, andoptional SAP analog audio signals and to convert the signals to adigital format. A stereo e.g., BTSC, encoder may be included that isconfigured to receive the digital format audio signals and encode themaccording the appropriate stereo sound standard. A video digitizingstage may be configured to receive a broadcast-compatible video signaland to convert the video signal to a digital format. A videoconditioning stage may be configured to receive the digital video signaland to produce a pilot signal. An audio FM modulator may be configuredto receive the digital combined audio signal and place it at a broadcastaudio signal frequency, creating a modulated digital audio signal. Avideo AM modulator may be configured to receive the digital conditionedvideo signal and place it at a broadcast video signal frequency,creating a modulated digital video signal. The system may include asummer that is configured to sum the modulated digital audio signal andthe modulated digital video signal to create a complete broadcastsignal.

In one embodiment, the television audio signal encoder may also includea digital-to-analog converter (DAC) configured to receive the completecolor broadcast signal and convert the complete color broadcast signalto an analog format. The system of claim may include at least oneanti-aliasing filter. The system may include at least one lineamplifier.

In accordance with another aspect of the disclosure, a computer programproduct residing on a computer readable medium may have a plurality ofinstructions stored thereon which, when executed by a processor, causethat processor to digitize and encode left and right audio signalsaccording to a stereo standard. The instructions may cause the processorto produce a combined audio signal and stereo pilot signal from abroadcast compatible video signal. The instructions may cause theprocessor to place the combined audio signal at a desired final signalcarrier frequency by frequency modulation. The instructions may causethe processor to place the video signal at a desired video signalcarrier frequency by amplitude modulation. The instructions may causethe processor to combine the audio and video signals to create combinedsignal on a transmission signal.

In one embodiment, the computer program product may include instructionsto convert the combined signal to an analog format. The computer programproduct may include instructions to provide the combined signal to atleast one anti-aliasing filter. The computer program product may includeinstructions to provide the combined signal to at least one lineamplifier. The computer program product may include instructions todigitize and encode a second audio program (SAP) audio signal accordingto stereo standard as part of the combined audio signal. The computerprogram product may include instructions to transmit the combined signalthrough a transmission medium.

In accordance with another aspect of the disclosure, a method may beprovided for producing a broadcast signal. A stereo pilot signal may beextracted from a broadcast compatible video signal. Left and right audiosignals may be digitized and encoded according to a stereo standard,e.g., BTSC. A combined audio signal may be formed. The combined audiosignal may be placed at a desired final signal carrier frequency byfrequency modulation. The video signal may be placed at a desired videosignal carrier frequency by amplitude modulation. The audio and videosignals may be digitally combined to create a combined digital signal ona transmission signal.

In one embodiment, the method may include converting the combineddigital signal to an analog format. The method may include providing thecombined digital signal to at least one anti-aliasing filter. The methodmay include providing the combined digital signal to at least one lineamplifier. The method may include digitizing and encoding a SAP audiosignal according to the BTSC standard as part of the combined audiosignal.

Additional advantages and aspects of the present disclosure will becomereadily apparent to those skilled in the art from the following detaileddescription, wherein embodiments of the present invention are shown anddescribed, simply by way of illustration of the best mode contemplatedfor practicing the present invention. As will be described, the presentdisclosure is capable of other and different embodiments, and itsseveral details are susceptible of modification in various obviousrespects, all without departing from the spirit of the presentdisclosure. Accordingly, the drawings and description are to be regardedas illustrative in nature, and not as limitative.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the disclosure itself may be more fully understoodfrom the following description when read together with the accompanyingdrawings. The drawings are not necessarily to scale, emphasis insteadbeing placed on the principles of the disclosure. In the drawings:

FIG. 1 is a block diagram representing a television signal transmissionsystem configured to transmit a television broadcast signal directlythrough a digital combination without an IF step.

FIG. 2 is a block diagram representing a television receiver system thatis configured to receive and decode the broadcast signal sent by atelevision signal transmission system, such as that shown in FIG. 1.

FIG. 3 is a block diagram representing a portion of the televisionsignal transmission system shown in FIG. 1 that combines a digitalstereo encoder with a digital video conditioner and a digital modulatorfunctional block according to the teaching herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a functional block diagram of a television signaltransmitter 10 is presented that processes audio and video content of atelevision signal for transmission to one or more reception sites. Thetransmitter 10 produces a broadcast television signal directly at aradio frequency through digital combination without an intermediatefrequency (IF) step. The audio content processed by the transmitter 10may comply with various television standards such as the BTSC standard,the A2/Zweiton Standard, the EIA-J standard, the NICAM standard, theDual FM standard, and others. The video content may comply with variousstandards such as the NTSC standard, the PAL standard, and the SECAMstandard, and variations of these. Variations of the PAL standardinclude the PAL I, B, G H, M, D, and N variations. Variations of theSECAM standard include the SECAM D, K, L, B, and G variations.

In the design shown in FIG. 1, a digital stereo audio encoding stage 24is combined with a digital video conditioning stage 60 and a digitalaudio/video modulator stage 26. Left and right audio signals areprovided on respective lines (e.g., conductive wires, cables, buses,etc.) 12 and 14. A secondary audio program (e.g., SAP) signal thatincludes additional signal information content (e.g., alternativelanguages, either as audio signals or subtitles for video viewing, etc.)may be provided by line 16. A fourth line 18 may provide a professionalchannel that would typically be used by broadcast television and cabletelevision companies. To transmit video content, video channel signalsare provided by a line 20 to a transmitter 22.

Signals from the audio channels are digitized and encoded to form stereosignals and then prepared for transmission. The stereo encoding stage 24may produce sum and difference signals from the left and right channelsignals and may use a pilot signal from the video signal(s). The stereoencoding stage may employ suitable stereo encoding such as described inU.S. Pat. No. 6,259,482, the contents of which are incorporated hereinby reference. Video conditioning stage 60 may perform signalconditioning on digitized video signals of channel 20.

Audio/video modulator stage 26 may receive the processed audio signals,e.g., sum signal and difference signals, and video signals and preparethe signals for transmission. Additional signals present for some stereostandards, e.g., a professional channel for BTSC, may also be preparedfor transmission by audio/video modulator stage 26. In this exemplarydesign, audio/video modulator stage 26 combines and provides the audioand video signals to transmitter 22.

In operation, the audio/video modulator stage 26 frequency modulates thestereo audio signals, placing them directly at a desired audiotransmission signal frequency. The video signals are amplitude modulatedby the audio/video modulator stage 26 and placed at a desired videotransmission signal frequency. The audio and video signals at theirrespective transmission frequencies are then digitally combined, forminga complete television broadcast signal. Operations of the audio/videomodulator stage 26 may be performed by utilizing a digital signalprocessor (DSP) or similar hardware techniques known to one skilled inthe art of television audio and video signal processing. Softwaretechniques known to one skilled in the art may likewise be used.

The signals of the broadcast channel may subsequently be transmitted,e.g., provided, for example, to an antenna (or an antenna system) 28,when the latter is needed for transmitting the signal. Various signaltransmitting techniques known to one skilled in the art of televisionsystems and telecommunications may be implemented by transmitter 22 andwhen needed antenna 28. For example, transmitter 22 may be incorporatedinto a cable television system (where an antenna is not needed), abroadcast television system, or other similar television audio and videocontent generation system.

FIG. 2 is a block diagram representing a television receiver system 30that is configured to receive and decode a television broadcast signalsent by a television signal transmission system, such as that shown inFIG. 1. The television receiver system 30 may include an antenna 32 (ora system of antennas) for receiving stereo compatible broadcast signalsfrom television transmission systems such as system 10 (shown in FIG.1). The system 30 is shown configured to receive BTSC audio signals butother stereo standards may of course be used.

For the receiver system 30, the received signals are preferably providedto a receiver 34, the latter being capable of detecting and isolatingthe television transmission signals. However, in some arrangementsreceiver 34 may receive the stereo compatible signals from anothertelevision signal transmission technique known to one skilled in the artof television signal broadcasting. For example, the television signalsmay be provided to receiver 34 over a cable television system or asatellite television network.

Upon receiving the television signals, receiver 34 conditions (e.g.,amplifies, filters, frequency scales, etc.) the signals and separatesthe video signals and the audio signals from the transmission signals.The video content is preferably provided to a video processing system 36that prepares the video content contained in the video signals forpresentation on a screen (e.g., a cathode ray tube, etc.) associatedwith the television receiver system 30. Signals containing the separateaudio content are preferably provided to a demodulator stage 38 thate.g., removes the modulation applied to the audio signals by televisiontransmission system 10. The demodulated audio signals (e.g., an SAPchannel signal, a professional channel signal, a sum signal, adifference signal) are preferably provided to a stereo, e.g., BTSC,decoder 40 that appropriately decodes each signal. When present, the SAPchannel signal is preferably provided a SAP signal decoder 42 and theprofessional channel signal is preferably provided to a professionalchannel decoder 44. A demodulated sum signal (i.e., L+R signal) ispreferably provided to a de-emphasis unit 46 that processes the sumsignal in a substantially complementary fashion to the processing bystereo encoding stage 24 shown in FIG. 1. Upon de-emphasizing thespectral content of the sum signal, the signal is preferably provided toa matrix 48 for separating the left and right channel audio signals.

The difference signal (i.e., L−R) is also demodulated by demodulationstage 38 and is preferably provided to a stereo, e.g., BTSC, expander 50that is included in stereo decoder 40. Stereo expander 50 complies witha suitable stereo standard, such as the BTSC standard, to condition thedifference signal. Matrix 48 receives the difference signal from stereoexpander 50 and with the sum signal, separates the right and left audiosignals into independent signals (identified in the figure as “L” and“R”). By separating the signals, the individual right and left channelaudio signals may be conditioned and provided to separate speakers. Inthis example, both the left and right audio signals are provided to anamplifier stage 52 that applies the same (or different) gains to eachsignal prior to providing the appropriate signals to a speaker 54 forbroadcasting the left channel audio signal content and another speaker56 for broadcasting the right channel audio content.

Digitized audio signals from a left, right, and SAP channel arepreferably provided over respective lines 62, 64, and 66 to stereoencoder 58. Specifically, signals from the left and right audio channelsare preferably provided to a matrix, such as described in U.S. Pat. No.6,259,482, the contents of which are incorporated herein by reference.The matrix calculates a sum signal (e.g., L+R) and a difference signal(e.g., L−R) from the digital audio signals. Typically operations of thematrix are performed by utilizing a digital signal processor (DSP) orsimilar hardware techniques known to one skilled in the art oftelevision audio and video signal processing. Alternatively, theoperations of the matrix may be partially or completely implemented withsoftware techniques known to one skilled in the art. Once produced, sumand difference signals (i.e., L+R and L−R) are encoded for transmission.

FIG. 3 is a block diagram representing a detailed portion of thetelevision signal transmission system shown in FIG. 1. Left and rightaudio signals 62, 64 are digitized by an analog-to-digital stage (A/D)70 within the stereo encoding stage 24. One or more suitable D/Aconverters may be used for this process. The digitized audio signal maythen be encoded according to the relevant stereo standard specification,e.g., BTSC, for example as described in previously mentioned U.S. Pat.No. 6,259,482. When present, an incoming SAP signal 66 may alsodigitized, FM-modulated, and combined with the stereo data to produce acombined audio signal. A stereo pilot signal 78 required for the stereoencoding process may extracted from the incoming video signal on thevideo channel 90.

An FM modulator 82 within the audio/video modulator stage 26 places thecombined audio signal directly at the carrier frequency at the desiredfinal audio signal. For example, the audio frequency carrier for cablechannel three according to the NTSC standard is located at the 65.75 MHzincrementally related carrier (IRC). Similarly, the audio frequencycarrier for cable channel four would be 71.75 MHz (IRC). In this way,the use of an intermediate frequency (IF) can be avoided.

Input video signals on video channel 90 are digitized by an A/D stagewithin the video conditioning stage 60. Video conditioner/combiner 80may be used to condition and combine the input video signals, producinga broadcast video signal. For example, video conditioner/combiner 80 maycombine the signals to form a CVBS signal. The videoconditioner/combiner 80 may act to limit the bandwidth of the combinedsignal and perform other signal conditioning, e.g., back-porchreferenced DC-restoration.

Once the broadcast video signal has been generated, a digital AMmodulator 86 can place the video at the proper video signal frequency.As an example, the video carrier frequency for NTSC cable channel threeis 61.25 MHz (IRC), and the video carrier frequency for NTSC cablechannel four is 67.25 MHz (IRC).

Once the audio and video signals have been placed on their respectivecarrier frequencies, they may be digitally combined by a summer 84 tocreate a complete transmission signal. The resulting combined digitaltelevision broadcast signal may then be passed through adigital-to-analog converter (DAC) 88 and then placed on the transmissionmedium, e.g., line to transmitter 22. Appropriate anti-aliasing filtersand line amplifiers may be used to improve signal quality and boost thepower of the. The DAC is preferably a high-speed device.

Accordingly, aspects of the present disclosure may offer advantages overthe prior art. Aspects may provide for the production of televisionbroadcast signals directly at a signal frequency of interest without theneed to use any intermediate frequency (IF) stages. Such architecturescan provide for decreased costs and increased reliability for thetelevision broadcasting.

In this example, stereo encoders, modulators, summers, and convertershave been described as being implemented with hardware components (andmay be manufactured, for example, as a single integrated circuit, andchip set, a hybrid circuit, or a circuit with discrete components),however, in some arrangements one or more operational portions of thestereo encoders, modulators, summers, and converters stages may beimplemented in software or a combination of both. Software code may beprovided in a suitable language, e.g., Verilog. This code may be storedon and retrieved from a storage device (e.g., RAM, ROM, hard-drive,CD-ROM, etc.) and executed on one or more general purpose processorsand/or specialized processors such as a dedicated DSP.

While the previous examples have made reference to particular stereostandards, e.g., BTSC, and video standards, e.g., NTSC, other standardsare within the scope of the present disclosure. For example, audiocontent may comply with various television standards such as the BTSCstandard, the A2/Zweiton Standard, the EIA-J standard, the NICAMstandard, the Dual FM standard, and others. The video content may complywith various standards such as the NTSC standard, the PAL standard, andthe SECAM standard, and variations of these. Variations of the PALstandard include the PAL I, B, G, H, M, D, and N variations, andvariations of the SECAM standard include the SECAM D, K, L, B, and Gvariations.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

1. A computer program product for producing a NTSC television signal andresiding on a computer readable medium having a plurality ofinstructions stored thereon which, when executed by a processor, causethat processor to: digitize and encode left and right audio channelsaccording to a BTSC stereo standard so as to produce a combined audiosignal; extract a stereo pilot signal from a broadcast compatible videosignal; place the combined audio signal directly at a desired finalcarrier frequency by frequency modulation without the use of anintermediate frequency signal; place the video signal at a desired videocarrier frequency by amplitude modulation; combine the audio and videosignals to create a combined digital signal suitable for transmissionthrough a transmission medium; convert the combined digital signal to ananalog NTSC format signal; and provide the NTSC format signal to atleast one anti-aliasing filter.
 2. The computer program product of claim1, further comprising instructions to provide the NTSC signal to atleast one line amplifier.
 3. The computer program product of claim 1,further comprising instructions to digitize and encode a SAP audiochannel according to the stereo standard as part of the combined audiochannel.
 4. The computer program product of claim 1, further comprisinginstructions to transmit the NTSC signal through a transmission medium.5. A method of producing a NTSC television broadcast signal with atelevision broadcast signal system, comprising: with a digital videoconditioner, extracting a stereo pilot signal from a broadcastcompatible video signal; with a digital stereo encoder, digitizing andencoding left and right audio channels according to the BTSC stereoaudio standard, wherein a combined audio channel results; with a digitalmodulator, placing the combined audio channel directly at a desiredfinal channel carrier frequency by frequency modulation without the needfor use of a signal of intermediate frequency; with the digitalmodulator, placing the video signal at a desired video channel carrierfrequency by amplitude modulation; with the digital modulator, combiningthe audio and video signals to create a combined digital signal on atransmission channel; converting the combined digital signal to a NTSCanalog format signal; and providing the NTSC analog format signal to atleast one anti-aliasing filter prior to transmission.
 6. The method ofclaim 5, further comprising providing the NTSC analog format signal toat least one line amplifier.
 7. The method of claim 5, furthercomprising digitizing and encoding a SAP audio channel according to thestereo standard as part of the combined audio channel.